Who is Lucia Soto?

Lucia Soto is an LAPD detective who had been a partner of Bosch's, when he was still part of the LAPD police force. During the events of the novel, Soto is forced to essentially be Bosch's opponent, as her Conviction Integrity Unit uncovers significant DNA evidence that appears to prove that Bosch had wrongfully convicted a murder suspect decades earlier. Soto subtly tries to help Bosch by leaking him documents related to the investigation, which he studies for clues until he is able to prove his innocence. After realizing that Bosch had not committed any wrongdoing, Soto both personally apologizes and then investigates another case as a favor to him.